It is common practice to grow aquatic organisms such as fish and the like in tanks or bag like structures for the commercial market.
One of the main problems of these systems is the tendency for sediment to build in the bottom of the tank or to be released into the surrounding waters and cause contamination detrimental to the process or the surrounding environment.
There have been numerous proposals and applied systems for cleaning aquaculture tanks. See for example, Canadian patent 1,117,385 issued Feb. 2, 1982 to Casey, Canadian patent 1,292,919 issued Dec. 10, 1991 to Ragnar et al. and Canadian patent applications, 2,000,443 published Apr. 12, 1990 by Arne et al., 2,072,357 published Jun. 20, 1991 by Jorgensen. See also U.S. Pat. Nos. 3,716,025 issued Feb. 13, 1973 to Lawson, 3,870,018 issued Mar. 11, 1975 to Furchtnicht, 4,141,318 issued Feb. 27, 1979 to MacVane, 4,171,681 issued Oct. 23, 1979 to Burger et al., 4,655,169 issued Apr. 7, 1987 to Paliola and U.S. Pat. No. 5,239,839 issued Mar. 15, 1994 to Jorgensen.
Many of the systems described in the patents use circulation of the water in the tank to deliver the sediment to a sediment outlet for example rotating flow in circular tanks to sweep the sediment toward the centre of the tank. U.S. Pat. No. 4,655,169 referred to above describes a system wherein conical grooves are provided in the bottom end of the tank and a circular flow is imparted into the water in the tank to cause the debris that settles to the bottom of the tank to be swept along the conical grooves into a collecting chamber or sump at the center of the tank. This system obviously relies substantially completely on gravity for separation of the sediment from the water i.e. the sediment falls by gravity to the bottom of the tank and the thus concentrated debris is swept along the helical bottom passages to a sump.
U.S. Pat. No. 5,639,595 issued Jun. 10, 1997 to Lunde et al. employs an annular chamber or sump surrounding a main tank outlet defined by an upper deck spaced from the bottom of the tank to provide a flow inlet extending around the full circumference of the sump. The sump is frusta-conical tapering towards a bottom end that is provided with a debris outlet adjacent to the central or axial main outlet passage from the tank. Outlet holes connect the sump with the main outlet passage at a position well above the debris outlet in the bottom of the sump. Water carrying debris flows into the chamber substantially radial around the full periphery of the chamber and towards the bottom and then flows back up and out through the outlet passages leading to the main passage. Debris falling from the water entering the sump is removed via the debris outlet. This system does not significantly concentrate the sediment for removal.
The centrifugal separation wherein circular flow at high angular velocity of a sediment containing liquid to apply centrifugal force to concentrate the higher density material adjacent to the outer wall of the chamber is well known, for example, in the pulp and paper art, for separation of fiber and shive from water or the mining industry for increasing the concentration of solids carried in the liquid streams.